During the automatic sorting of flat mailings in distribution order on a sorting machine in a plurality of passes, in the normal case all the mailings to be distributed by the mailman on one day have to be put one after another into the sorting machine. However, a relatively large time window is needed for this. If this is not available, then some of the mailings supplied must already previously be sorted in distribution order and then the sorting of the remainder of the mailings supplied in distribution order is carried out. The two pre-sorted stacks are then combined to form a single stack sorted in the distribution order. For this purpose, each stack is separated again. The separation is carried out in such a way that the mailings led together in a transport stream are transported in the distribution order. This transport stream opens into a stacking device in which, by means of continuous scanning, one or more part stacks with mailings in the distribution order are produced.
As a result of separation errors, for example double extractions, or erroneous mailings, the extraction sequence predefined on the basis of the known destination addresses of the pre-sorted stacks can lead to wrong orders in the combined mailing stream and the entire following stack section.
This erroneous sorting can be detected by using a detection unit, arranged on the transport path after the separating devices, in order to determine the destination addresses. The wrongly allocated mailings are then sorted into a special compartment and then have to be sorted manually into the stack produced.
In order that as few mailings as possible are sorted into the special compartment as wrongly allocated, the detection unit should be arranged as close as possible to the separating device. However, this is possible only to a restricted extent, since an alignment section must always be located upstream of an economical detection unit, that is to say the minimum distance between separating device and detection unit is approximately 2 m. The result of this in turn is that, when a fault is detected, the mailings already located in the alignment section can no longer be influenced and have to be inserted manually into the sorted stack, which is costly and time-consuming.